Rc oscillator with comparator offset compensation

Abstract

A comparator-based oscillator generates an output frequency that is relatively independent of comparator offset voltages. Charging/discharging circuitry controls the comparator input voltage, and logic circuitry generates the oscillator output (e.g., clock) signal and controls the charging/discharging circuitry. During an oscillator charging cycle, the charging/discharging circuitry drives the voltage at the comparator input node from a relatively low initial charging voltage level up to the comparator reference voltage. During an oscillator discharging cycle, the charging/discharging circuitry drives the voltage at the comparator input node from a relatively high initial discharging voltage level down to the comparator reference voltage. The initial charging and discharging voltage levels depend on the comparator reference voltage, such that a comparator offset voltage directly affects the initial charging and discharging voltage levels, thereby keeping the output frequency relatively unchanged.